This invention relates in general to metrology devices and in particular to metrology devices that may be used to measure diffracting and anisotropic structures.
The reduction on the size of microchip components requires new metrology technologies for monitoring critical dimensions (CDs). Optical metrology techniques are particularly advantageous because they are non-destructive, non-invasive, economical and compact. Certain structures are particularly difficult to accurately measure. For example, complex line profiles, such as sloping sidewalls, undercut sidewalls, and notches in the sidewalls can be difficult to measure accurately.
Thus, what is needed is an optical metrology tool to measure quickly and accurately diffraction gratings, including diffraction gratings having complex cross- sectional profiles.
A normal incidence polarimeter is combined with an oblique incidence polarimeter, in accordance with an embodiment of the present invention, to provide an accurate characterization of complex grating structures, e.g., structures with sloping sidewalls, notches, and/or multiple underlying layers. In one embodiment, spectroscopic polarimeters are used.
The normal incidence polarimeter includes a polarizing element that is in the path of the normal incidence light beam. The normally incident light passes through the polarizing element before reaching the sample and after being reflected off the sample. The oblique incidence polarimeter includes a polarization stage generator in the light path before the sample and a polarization state detector in the light path after the sample.
The metrology device may use a single light source to produce the normally incident light beam and the obliquely incident light beam. Alternatively, multiple light sources may be used. In addition, the metrology device may use a single spectrophotometer to detect both the obliquely incident light beam and the normally incident light beam after being reflected off the sample. Alternatively, the normal incidence polarimeter and the oblique incidence polarimeter may use separate spectrophotometers.